There are many oral therapies for erectile dysfunction, but the only approved medication in the US is the PDE 5 enzyme inhibitor sildenafil Viagra. In addition, consider the information below. This means that vardenafil Levitra should act longer than sildenafil Viagra but the clinical significance is not known. Which Lasts Longer? Sexual activity is not a major contributor to the risk of a heart attack. Side effects Side effects of oral ED medicines are often mild.Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes . Viagra takes around 30 minutes to become effective and lasts about 4 hours. Cialis lasts much longer — up to 36 hours in some cases. Stendra can start doing its thing in as little . The vagina and clitoris also contain PDE5. So, if a female takes Viagra, the drug may increase blood flow to these areas. However, female genitals contain less .